Neuroscience: Trial by sympathy

Nature Communications

March 28, 2012

Brain regions related to moral conflict are activated when jurors, who are deciding on the severity of a sentence, are presentenced with mitigating circumstances. The finding, reported in Nature Communications, suggests that the severity of a sentence given to criminals may depend on the circumstances under which the crime was committed. The work may help the legal system understand how potential jurors make decisions, and contributes to the growing debate about what role emotional evidence can and should have in trials.

The activation of unique brain circuits is crucial to how we make decisions. These decisions are often affected by different emotional states. Prosocial emotions, such as sympathy, have been shown to affect decision making, however there is currently no direct cognitive and neural evidence for how sympathy is translated into legal outcomes.

Makiko Yamada and colleagues exposed volunteers acting as jurors to scenarios adapted from actual murder cases in Japan. During each case they were presented with mitigating circumstances, some that would induce sympathy and some that would not. After jurors rated each case for level of sympathy felt, the team noted that high sympathy ratings correlated with the activation of moral conflict regions of the brain, such as the dorsomedial prefrontal cortex and precuneus. They show that this subsequently affected behaviour when it came to making hypothetical sentence reduction decisions.

This work uncovers neural evidence for a close relationship between sympathy and mitigation, which then translates into behaviour in a courtroom situation. It is, however, yet to be studied whether these findings are replicated in jurors from nations where guidelines related to mitigating circumstances in a court of law differ.